1. Field of the Invention
The present invention relates to a spin-stabilized projectile having an aerodynamic braking device in a front region thereof, wherein the braking device can be radially extended along its trajectory from a launch condition into an axially symmetrical operative position.
2. Discussion of the Prior Art
The invention concerns a spin-stabilised projectile as set forth in the classifying portion of claim 1.
The projectile of the general kind set forth is known from WO 98/01719 A1. That involves arranging semicircular plates in the plane of separation between the projectile body and the projectile tip, wherein the semicircular plates, in mutually axially overlapping relationship, are displaced relative to each other azimuthally around the longitudinal axis of the projectile. They can be extended radially with respect to that longitudinal axis from their launch position within the contour of the projectile into the axially symmetrical operative position thereof in order then to shorten the ballistic trajectory as a result of the increase in aerodynamic resistance. Installation of the mechanism for displacing the plates between the two positions thereof and stable retention of the plates which are subjected to a heavy flexural loading in the extended position by virtue of the air flow thereagainst, precisely in the plane, which is critical in terms of structure and function, of the transition from the tip into the body of the projectile, does however involve serious construction risks, especially as that cross-sectional plane in itself is already fully occupied with the fuse components which here extend from the tip into the body of the projectile.
In comparison, it is known from DE 36 08 109 A1 to provide a braking device for a spin-stabilised projectile, in the central region thereof, in the form of a peripherally extending recess for forming stowage chambers for a cloth which, by virtue of the release of centrifugal weights which can be flung radially away, is opened out radially to form an annular braking sail around the peripheral surface of the projectile. The position thereof, in relation to the projectile body, admittedly basically affords greater structural freedom in regard to arranging the braking device when it is not yet extended into the operative position and the drive elements for moving it into the operative position, under the effect of centrifugal force; however, this arrangement requires total reconstruction of the projectile because of serious effects on the load-bearing structure and the payload space thereof. Another disadvantage is that there is no guarantee that the textile ring retains its shape, when the flow of air thereagainst is asymmetrical.
In consideration of those aspects, the technical object of the present invention is that of equipping a projectile of the general kind set forth, with an easily activatable, operationally reliable, aerodynamic braking device which is uncontrolled (and which therefore has an on-off or two-position characteristic) but which nonetheless is highly effective.
In accordance with the invention, as set forth in the characterising portion of the main claim, that object is essentially attained in that provided as the aerodynamic braking device approximately in the central region of the projectile tip is a flap system which is in the form of sectors of a ring and which is pivotable out of the launch position in opposite relationship to the afflux flow of air thereagainst into a geometrically defined operative position and which is coupled there in a peripherally extending recess to the wall of the fuse casing. As the fuse is disposed in the tip of the large-calibre munition which is of interest here, for cannon artillery, the complete tip is designed for disassembly, that is to say, it is mounted on the body of the projectile in such a way as to be readily interchangeable. In that way, the conventional munition which is in use can also still be subsequently equipped with this braking device for influencing the projectile trajectory, insofar as the conventional projectile tip is simply replaced by another tip with the braking elements.
Admittedly, it is known in this respect from DE 198 45 611 A1 for trajectory control in the case of non-spin and in the case of fin-stabilised projectiles to be effected by correction elements being extended in axially asymmetrical relationship to a greater or lesser degree out of a separate correction unit, from the missile body or also from the fuse; in that arrangement however, a quite considerable installation space is required for the control, which is always continuous in that case, in respect of the correction elements and the adjusting force acting thereon, and such installation space is only available with difficulty, even in the event of major redesign in fuse systems which are in use.
In accordance with the present invention in contrast the centrifugal force on the spin-stabilised projectile causes the flap-shaped sectors of the braking device to pivot out in an unbraked swinging movement, into a star-shaped, substantially radially oriented operative position which is afforded by virtue of the force equilibrium in respect of the dynamic pressure forces and centrifugal forces acting on the braking elements. That means that there is no need to provide for structural elements operative for actively extending the braking device, in the interior of the projectile tip, so that this braking system can be mounted to the projectile relatively far forwardly around the tapered region of the tip where the aerodynamic braking effect is at the greatest and therefore the braking flaps can be relatively short. The position as far as possible in front of the plane of separation in relation to the projectile body is also desirable because there the interior of the tip is practically not required for fuse functions and because that region is also structurally insignificant in terms of the flexural stiffness of the projectile overall, that is to say, it certainly tolerates a weakening of the fuse casing due to radial openings for mounting the pivotal shafts for the braking flaps therein. In this case, the individual flap-shaped braking sectors are not pivoted outwardly until they come to bear against an abutment which is fixed with respect to the casing, because that would give rise there to critical stability problems, especially in relation to an afflux flow of air which possibly acts in the extension direction. In the case of munition involving a slight amount of spin, the outward pivotal movement of the braking elements can be promoted by leg springs which are disposed therebehind and which are tensioned between the braking elements and the casing of the projectile tip. Desirably, in any event, the arrangement involves a simple latching action to prevent a return movement of the flap sectors of the braking device, which swing freely in their operative position, so that, once the braking device has reached its geometrically defined operative position, the braking device reliably remains in that operative position immediately and even under fluctuating afflux conditions, in the interests of a stable braking characteristic.
In the launch position of being pivoted into the casing, the flap-shaped braking elements scarcely project radially. Therefore they may not be so wide that for example at their pivotal mounting, they project laterally beyond the peripheral surface of the fuse tip. Therefore, comparatively narrow flaps are pivotably mounted in mutually displaced relationship in the peripheral direction, on pin-like pivotal shafts which are mounted asymmetrically. Spring supports can be arranged under each two mutually adjacent flaps in order to promote uniformly occurring extension of all flaps, over the entire periphery of the tip, by virtue of the flaps mutually assisting each other.
The flap-shaped braking elements which are in the form of sectors of an annular disc and which in their launch position are retracted against the fuse casing parallel to the peripheral surface of the cap cannot therefore overlap each other to such a degree in the peripheral direction of the fuse casing that, in the radially extended position, in a front view, they define a closed, radially wide ring around the tip, and for that reason in the extended position the arrangement does not provide an uninterrupted annular disc but a widely spread spoke-like structure. The aerodynamic braking action thereof however is only slightly reduced in comparison with a closed annular disc because eddy and turbulence losses at the transitions from the closed sectors to the gaps therebetween result in additional braking effects. The braking action however can be still further increased if the intermediate spaces between the sectors of the annular disc are bridged over by flexible elements, for example by textile portions, which are extended between the sectors upon extension of the flaps. In that respect, a simpler pivotal mounting, with a braking device structure which is geometrically and mechanically stable, is afforded if the flap-shaped sectors of the annular disc are narrowed to form thin spokes which impart geometrical stability, even under fluctuating aerodynamic influences, to a textile structure which is extended in the form of an annular disc in the manner of an umbrella, as a result of a radial bracing action. The textile ring which is braced by the spokes can then be still further enlarged by an edge portion which extends therearound in an unbraced condition, in order to optimise the braking engagement surface area for the afflux flow.
If on the other hand the substantially textile uninterrupted structure of the braking device is to be replaced by an annular surface which is mechanically more stable as it is metallically closed in the afflux direction, as in fact cannot be achieved without gaps due to the width of the flap-shaped sectors alone, then those braking elements can be provided at both sides, at their radially extending longitudinal edges of the sectors in question, with triangular spring plates which alternately overlap each other in the inwardly folded condition of the sectors, being elastically adapted to the peripheral surface curvature of the projectile tip, and in the stretched extended condition just cover over in pairs the openings, which in themselves are free, between the flaps.